Technical Field
The present disclosure relates to an image forming apparatus and a process cartridge.
Description of the Related Art
In a typical electrophotographic image forming apparatus, residual toner particles remaining on a photoconductor or image bearer without being transferred onto a transfer sheet or intermediate transfer medium are removed by a cleaner. The cleaner generally contains a cleaning blade having a strip-like shape for its simple configuration and excellent cleaning ability. Such a cleaning blade is typically composed of an elastic body blade having a strip-like shape which may be made of polyurethane rubber.
The cleaning blade is configured to hold and scrape off residual toner particles remaining on the image bearer to remove them from the image bearer while the base end of the elastic body blade is supported by a support and the tip ridgeline part of the elastic body blade is pressed against the peripheral surface of the image bearer.
When the elastic body blade, which may be made of polyurethane rubber, is brought into contact with the image bearer to clean the image bearer, the tip of the blade is pulled in the direction of movement of the image bearer due to the frictional force generated between the image bearer and the cleaning blade, thereby causing stick-slip motion. If the image bearer is cleaned during the occurrence of stick-slip motion, toner particles will pass through between the elastic body blade and the image bearer, resulting in defective cleaning. In addition, toner particles or external additives thereof will be rubbed against the image bearer to be firmly adherent to the image bearer.
On the other hand, the toner typically contains a release agent. In a case in which the release agent is positioned near the surface of the toner for the purpose of accelerating exposure of the release agent, the occurrence of offset phenomenon can be prevented, but the release agent may become adherent to other members while the toner is being stirred in a developing device. The toner may be pressed against carrier particles or photoconductors and become firmly adherent thereto. This phenomenon is hereinafter referred to as filming. The filming phenomenon is likely to deteriorate developability.
Thus, the release agent should be protected inside the toner when the toner is being stirred or stored. At the same time, the release agent should be efficiently exposed at the surface of the toner to express releasability from the fixing member in such a short time during which the toner passes through the fixing member.
Many attempts have been made to determine a proper dispersion particle diameter for the release agent dispersed in the toner for preventing the occurrence of the offset problem while maintaining toner productivity. It is generally very difficult to contain the wax in the form of fine particles inside the toner without exposing them at the surface of the toner because the wax particles are inevitably finer than the toner particles.
From the standpoint of giving resistance to the offset phenomenon (hereinafter “hot offset resistance”) to the toner, it is more effective that the release agent exists in the form of a relatively large block rather than in the form of fine particles locally distributed over the toner. If the release agent in the form of a large block is achieved by excessively increasing the content of the release agent, the toner will deteriorate in strength and become easy to get crushed, deteriorating resistance to the filming phenomena.
Accordingly, there has been a demand for a toner which achieves a good combination of filming resistance and offset resistance with using a small amount of release agent.